The invention relates to electronic semiconductor devices and circuits, and, more particularly, to vertical field effect transistors and methods of fabrication.
Various semiconductor device types have been used for power handling: junction field effect transistors (JFETs), field-controlled diodes, power metal oxide-semiconductor field effect transistors (power MOSFETs), bipolar transistors, MOS gated thyristors, and insulated gate transistor (IGT). See Baliga, Modern Power Devices ch.4 (Wiley-Interscience 1987). Power devices ideally have low forward voltage drop, high switching speed, and low control power consumption; and the vertical field effect transistors (VFET) can provide these requirements. See Sze, Physics of Semiconductor Devices p.357 (Wiley-Interscience, 2d Ed., 1981) and Campbell et al, 150 Volt Vertical Channel GaAs FET, IEDM Tech. Dig. p.258 (1982). These references show a device with parallel buried p+ gate fingers and vertical carrier flow through n type channels between the gate fingers; the bias of the gate modulates the current flow. Increased power handling may conveniently be achieved with multichannel devices. These devices may operate with unsaturated current-voltage (I-V) characteristics. The use of gallium arsenide (GaAs) rather than silicon for the semiconductor material reduces the on-resistance of such VFETs due to the higher electron mobility. See Baliga, 40 IEEE Elec.Dev.Lett. 455 (1989) and Shenai et al, Optimum semiconductors for high-power electronics, 11 IEEE Elec.Dev.Lett. 520 (1990).
Variations of the vertical FET with recessed surface gates appear in Tantraporn et al, U.S. Pat. No. 4,129,879, Frensley et al, Design and Fabrication of a GaAs Vertical MESFET, 32 IEEE Tr.Elec.Dev. 952 (1985), Campbell et al, Trapezoidal-Groove Schottky-Gate Vertical-Channel GaAs EFT (GaAs Static Induction Transistor), 6 IEEE Elec.Dev.Lett. 304 (1985), Mori et al, A High Voltage GaAs Power Static Induction Transistor, Extended Abstracts of the 19th Conference on Solid State Devices and Materials, Tokyo, 279 (1987), and Hong et al, . . . 29 Jap.J.Appl.Phys. L2427 (1990).
Power transistors in switching power supplies frequently have an accompanying switching-aid circuit, called a snubber circuit, to lessen switching stresses and losses. A turn-off snubber circuit may be a parallel diode and resistor in series with a capacitor, the circuit is connected between the collector and emitter of a power bipolar transistor or the source and drain of a power MOSFET.
However, such VFETs have problems including difficulties of fabrication and enhancing performance.
Power transistors in switching power supplies frequently have an accompanying switching-aid circuit, called a snubber circuit, to lessen switching stresses and losses. A turn-off snubber circuit may be a parallel diode and resistor in series with a capacitor, the circuit is connected between the collector and emitter of a power bipolar transistor or the source and drain of a power MOSFET.